Radio Shack 26-1061 User manual

Radio /hack
Service m
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MODELIDE
MICROCOMPUTER
Catalog Numbers 26-1061/1062/1063
CUSTOM MANUFACTURED IN U,S,ArBY RADIO SHACkHa DIVISION OF TANDY CORPORATION
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TABLE OF CONTENTS
SECTION PAGE
NUMBER NUMBER
IINTRODUCTION .1
System Overview ...... . 3
II DISASSEMBLY/REASSEMBLY 5
Disassembly •
Reassembly 9
III CPU CIRCUIT BOARD 11
Technical Description 13
Video Sync Circuits ,13
Processor ,.,13
RAM 13
Address Decoding 14
Memory Map 14
10 PORT Description 15
Video 16
Keyboard 17
Cassette Interlace 17
Line Printer and Real Time Clock 18
10 Bus 18
Adjustments and Jumper Positions 18
Model III 10 Bus Detailed Description 19
Model III PORT Bits 21
CPU Module Parts List 25
IV FLOPPY DISK INTERFACE 41
Technical Description 43
Control and Data Buffering 43
Non -Maskable Interrupt Logic 43
Drive Select Latch and Motor On Logic 43
Wait State Generation and WAITIMOUT Logic 44
Clock Generation Logic 44
Disk Bus Selector Logic 44
Read/Write Data Pulse Shaping Logic 44
Disk Bus Output Drives 44
Write Precompensation and Clock Recovery Logic ... 44
Floppy Disk Controller Chip 45
Adjustments and Jumper Options 45
Floppy Disk Interface PC Board Parts List 49
VRS-232C CIRCUIT BOARD 53
RS-232C Technical Description 55
Pin -Out Description 56
Port and Bit Assignments ,57
RS-232C PC Board Parts List .,-62
VI POWER SUPPLY 65
Functional Specifications 67
Troubleshooting 67
Set- Up Procedures 67
Visual Inspection 67
Start-Up 68
No Output 68
Performance Test 69
Power Supply Component Values 70

TABLE OF CONTENTS (Cont'd)
SECTION
NUMBER
VII
VIM
IX
PAGE
NUMBER
VIDEO MONITOR 73
Functional Specifications 75
Service Adjustments 77
ILLUSTRATED PARTS CATALOG 79
Illustrated Parts Catalog Parts List 86
MINI-DISK DRIVE 91
General Description 93
Introduction .,93
Important Notice 93
Physical Description 93
Functional Description 93
Interface Connections ....,.,., 93
Physical Checkout 94
Mounting the Disk Drive 96
Resistor Termination 96
Flat Ribbon Cable Assembly 96
Theory of Operation 97
Introduction -.97
Organization of the Disk Drive :.,,.. 97
Functional Block Diagram Description 97
Index Pulse •.*97
Write Protect 97
Track 00 Switch 97
Spindle Drive 97
Positioner Control ,97
Data Electronics ,93
Data Recording ,.,.,99
Data Reproduction . , 99
Operation 101
Interface Electronics Specifications 101
Input Control Lines 101
SELECT Lines (DS1* -DS4*) 101
Drive Motor Enable (MOTORONl 101
Direction and Step {DIR*} (STEP*) 101
Compensated Write Data (CWD) 101
Write Enable (WG*) 101
Side Select (SDSEL) 103
Output Status 103
Index Pulse (IP*) 103
TRACK 00 (TRK0") 103
Write Protect (WPRT*> .103
Read Data (RD*> 103
Maintenance 105
Physical Description of the PC Boards 105
Circuit Board Test Points 105
Option Select 105
Input Line Terminations 105
Preventive Maintenance 108
Cleaning the Head 108
Alignment and Adjustment 108
Drive Motor Maintenance 108
Carriage Movement Check 108
Head Radial Alignment/CE Alignment 109
Track 00 Alignment 110
Index Sector Adjustment 110
Head Amplitude/Compliance Check 111

TABLE OF CONTENTS (Cont'd}
SECTION PAGE
NUMBER NUMBER
Final Check 111
Disk Controller Board Parts List ,., . ,112
Servo Board Parts List (Non-Linear) 116
Servo Board Parts List (Linear) ,117
Illustrated Parts Catalog Parts List 119
LIST OF ILLUSTRATIONS
FIGURE PAGE
NUMBER TITLE NUMBER
SECTION I-INTRODUCTION
1TRS-80 Model III Block Diagram 4
SECTION III -CPU CIRCUIT BOARD
1CPU Timing Diagram ,,,,13
2Video Timing Diagram ,16
310 Bus Timing Diagram 20
4CPU Printed Circuit Board —Component Side 23
4CPU Printed Circuit Board -Circuit Side 24
5A Model III CPU Schematic Diagram -
Video and Horizontal Sync Circuits 31
5B Model III CPU Schematic Diagram —Processor Section 32
5C Model III CPU Schematic Diagram -RAM Section 33
5D Model III CPU Schematic Diagram —
Address Decoding Section 34
5E Model III CPU Schematic Diagram —Video Section 35
5F Model III CPU Schematic Diagram -Keyboard Section 36
5G Model III CPU Schematic Diagram —
Cassette Interface Section 37
5H Model III CPU Schematic Diagram —
Line Printer and Real Time Clock Section ,38
EJ Model Ml CPU Schematic Diagram -I/O Bus Section 39
SK Model III CPU Schematic Diagram -
RS-232C Interface and FDC Interface Connections 40
SECTION IV -FLOPPY DISK INTERFACE
1FDC Board to CPU Board Signal Description 46
2Floppy Diik Interface PC Board -Component Side 47
2Floppy Disk Interface PC Board -Circuit Side 48
3Model III Floppy Disk Interface Schematic 51

FIGURE
NUMBER
1
2
3
4
LIST OF ILLUSTRATIONS (Cont'd)
PAGE
TtTLENUMBER
SECTION V-RS-232C CIRCUIT BOARD
1RS-232C Board to CPU Board Signal Description 59
2RS-232C PC Board -Component Side ,...60
2RS-232C PC Board -Circuit Side 61
3Model III RS-232C Schematic Diagram 63
SECTION VI -POWER SUPPLY
Test Set-Up •<>7
Q2 Collector Waveform 68
Q2 Base Waveform 68
Power Supply Schematic Diagram 71
SECTION VII -VIDEOMONITOR
1Video Monitor Printed Circuit Board 76
2Deflection Yoke Assembly 77
3Video Monitor Assembly Schematic Diagram 7S
SECTION VII I-ILLUSTRATED PARTS CATALOG
Outer Case Assembly -**1
Case Top Assembly ^2
Base Plate Assembly 83
Metal Chassis Assembly *|4
So
1
2
3
4
5Disk Drive Assembly
SECTION IX -FLOPPY DISK DRIVE
1PC Board Component Locations (Logic Board) 94
1APC Board Components Locations {Servo Boards) 95
2Resistor Termination -^6
3Cable Assembly -Connector Pin Removal Chart ... 96
4
5
6Write Timing Diagram
8Interface Configuration iM
9
10
11 "Cat's Eyes" Pattern :M
12 Radial Adjustment ltJJ
13
14
15
16 Upper Arm and Carriage !
17
13
13
19 Servo Board Schematic 122
20 Mini-Disk Drive Schematic (new board} 123
20 Mini-Disk Drive Schematic (new board) 124
Functional Block Diagram 98
FM Recording S8
Write Timing Diagram 10°
Read Timing Diagram -10°
Interface Configuration 101
Logic Board Test Points and Connector Locations 106
Servo Board Connector Locations 107
Track <WJ Stop Adjustment
Index Sector Timing
Index Adjustment '10
Upper Arm and Carriage '
1'
Illustrated Parts Catalog -Exploded View 118
Mini-Disk Drive Schematic (Sheet 1) •120
Mini-Disk Drive Schematic (Sheet 2) 121

LIST OF TABLES
TABLE PAGE
NUMBER TITLE NUMBER
SECTION V-RS-232C CIRCUIT BOARD
BRG Programming Table ,,..,... 65
SECTION VI -POWER SUPPLY
1Load Board Values gg
2Voltage and Ripple Specifications ,,.,69
SECTION IX -MINI-DISK DRIVE
1Interface Connector Pin Assignments 102
2Power Connector Pin Assignments 102

SECTION I
INTRODUCTION

SYSTEM OVERVIEW
The Radio Shack TRS-80 Model III Microcomputer is an enhanced version of Radio Shack's popular TRS-80 Microcom-
puter (Model I). The TRS-80 Model III is software compatible with the Model Iso that owners of either system can take
advantage of the large number of programs available.
Features of the TRS-80 Model III which are common to the TRS-80 Model Iinclude:
•Availability of Level Ior Level II BASIC in ROM
•Full size typewriter style keyboard
•A12-inch video display
•Built-in cassette interface
•Character display of 16 lines of 64 characters
•Graphics under control of BASIC (128 Hx48 V)
•ULrecognized construction
In addition, the Model III has the following standard features:
•12-key numeric keypad for rapid entry of numbers
•Rugged cabinet housing keyboard, electronics, video display, and power supply
•Direct drive video monitor for Improved resolution
•Internal power supply
•Parallel printer port for use with Radio Shack printers
Several other features are available when Level II BASIC is used; features such as: real time clock, upper and lower case
characters, RAM internally expandable to 4SK bytes, I/O port for peripheral expansion, and cassette interface available
with 500 and 1500 baud rates.
Optional peripherals for the TRS-80 Model III include disk drives (two built-in, two external) with double density for
increased storage capacity, and abmtr-in RS-232 serial interface for communications and peripheral interface,
The Block Diagram shows the various internal components and connections of the Model III Microcomputer.